Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7882282 | Acta Materialia | 2014 | 12 Pages |
Abstract
A detailed study has been carried out on γⲠ(AlAg2) precipitates in Al-Ag and Al-Ag-Cu alloys to reconcile the conflicting reports on chemical ordering and stacking faults in this phase. High-angle annular dark-field scanning transmission electron microscopy and convergent beam electron diffraction show no indication of chemical ordering on alternate basal planes of γⲠprecipitates in alloys aged at 473 K for 2-23 h. Precipitates were visible as Ag-rich regions with 1-13 face-centred cubic (fcc) â hexagonal close-packed stacking faults, corresponding to γⲠplatelets with thicknesses ranging from 0.69 to 6.44 nm. There were no systematically absent thicknesses. Growth ledges with a riser height equal to the c-lattice parameter (0.46 nm) were directly observed for the first time. Genuine stacking faults within the precipitates were extremely rare and only observed in thicker precipitates. In precipitates with 1-3 stacking faults there was also substantial Ag in the surrounding fcc layers of the matrix, indicating that Ag strongly segregated to the broad, planar precipitate-matrix interfaces. This segregation is responsible for previous reports of stacking faults in γⲠprecipitates. The results indicate that the early stages of γⲠprecipitate growth are interfacially controlled.
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Julian M. Rosalie, Christian Dwyer, Laure Bourgeois,